Investigators view the remains of a Route 63 bridge that collapsed over the Naugatuck River and Metro North train tracks in downtown Naugatuck, Tuesday morning, June 15, 2010. The bridge, which had been replaced by an adjacent span, was in the process of being demolished. less

Investigators view the remains of a Route 63 bridge that collapsed over the Naugatuck River and Metro North train tracks in downtown Naugatuck, Tuesday morning, June 15, 2010. The bridge, which had been ... more

Workers at the scene of a Route 63 bridge that collapsed over the Naugatuck River and Metro North train tracks in downtown Naugatuck, Tuesday morning, June 15, 2010. The bridge, which had been replaced by an adjacent span, was in the process of being demolished. less

Workers at the scene of a Route 63 bridge that collapsed over the Naugatuck River and Metro North train tracks in downtown Naugatuck, Tuesday morning, June 15, 2010. The bridge, which had been replaced by an ... more

NAUGATUCK -- OSHA officials and state police said it will take weeks to determine why a 100-foot section of a state highway bridge suddenly collapsed Tuesday, seriously injuring a construction worker who fell 35 feet.

About 6:30 a.m., a section of the Salem Bridge, which crosses the Naugatuck River, broke away from the 586-foot span, sending the construction worker, who was in an excavator, to the ground.

Kowalski said his office dispatched two investigators soon after it was notified of the collapse.

Brunalli Construction, which is replacing the bridge for $23.5 million, on Tuesday had settled several record-keeping violations OSHA uncovered at the Naugatuck site during a November inspection.

Last year Brunalli paid $181,000 to settle alleged safety violations -- failing to protect workers against falls, drowning and other hazards -- OSHA found in 2008 during an inspection of the company's project to replace a bridge over the Housatonic River in Falls Village.

Brunalli was also cited for alleged violations four other times in the last 10 years, including in 2003, when the firm had a contract to replace a bridge on I-95 where four Yale University students died in a car accident.

A lawsuit against the DOT, which named Brunalli as a defendant for allegedly knocking out a light on the highway where the students died, was dismissed in 2009.

Brunalli officials declined comment when contacted by phone. According to various reports, Brunalli Construction was founded in 1963 and specializes in bridge construction.

"I can tell you that we haven't had any issues with Brunalli in the past, and they have always performed work to our satisfaction," said Kevin Nursick, spokesman for state DOT.

Nursick said Brunalli is the prime contractor on six active projects in the state, all bridges, and subcontractor on three active projects. It has completed six projects in the last five years, including at least five bridges.

Nursick said that DOT construction-inspection staff was on the job site and witnessed the incident.

"We're there for the protection of the general public and to make sure the design plans are met," Nursick said. "The safety of the contractors and their staff falls on their shoulders. We're not the authority for contractual-worker safety."

He said OSHA is responsible for site safety.

The last time the DOT inspected the bridge was toward the end of 2008. It was rated "5" for superstructure, "4" for substructure, and "4" for the deck, on a scale of 1 to 9. A 4 is poor and 5 is fair.

"It's not a safety rating," Nursick said. "It's a condition rating. If a bridge is unsafe, it's closed until it's safe. Exactly what happened here is to be determined. It was not open to the public. It was closed for active demolition."

Lt. J. Paul Vance, Connecticut State Police spokesman, said an initial investigation found that moments before the collapse Brunalli had an excavator and some laborers on the deck of the bridge, and the excavator operator sensed trouble.

"The operator had concerns and ordered the laborers off the bridge," Vance said. "He reported his concerns to his foreman and was trying to get the machine off the bridge."

But he couldn't get the large piece of machinery off the span before the girders on the east side tore loose and, as Vance described it, "he rode the bridge down."

The span on the north side of the bridge partially collapsed onto an access road that connects the playing fields of Breen Field. The remaining section of the 586-foot bridge that spans the river appeared intact. And the new southern structure carrying Route 63 remained standing.

As a precaution, Metro-North replaced Waterbury Branch trains with bus service during the morning. The railroad tracks run under the bridge where the section came crashing down. No debris fell on the tracks and service resumed in mid-afternoon.

Naugatuck firefighters and police and state police responded to the scene. Vance said the athletic fields near the bridge will be off limits. State DOT workers with bridge inspection equipment were dispatched to the scene, where they joined other hard-hatted crews from OSHA, Metro-North and the state Fire Marshal's Office.

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The bridge was built in 1961. Naugatuck Mayor Bob Mezzo, who is serving his first term, said the bridge's replacement has been on the town's capital project list for years, but funding only became available under the recent Recovery Act.